1. Field of the Invention
The present invention relates to power supply processing for power amplifiers.
2. State of the Art
High-efficiency power amplifiers (PAs), including radio frequency (RF) power amplifiers of a type used in RF transmitters, may be based on switch-mode techniques in which a transistor of a final amplification stage is driven between two states, a hard-on state and a hard-off state. In switch-mode operation, the output power of the final amplification stage is determined primarily by the power supply to the final amplification stage. In order to perform output power control, therefore, a mechanism is required to vary the power supply to the final amplification stage. One representative patent describing switch-mode PA techniques and corresponding power supply processing techniques is U.S. Pat. No. 3,900,823 entitled AMPLIFYING AND PROCESSING APPARATUS FOR MODULATED CARRIER SIGNALS, issued Aug. 19, 1975, incorporated herein by reference.
Three principle issues are raised with regard to power supply processing. One issue is the speed with which the power supply can be varied. Another issue is efficiency, or the extent to which losses incurred in power supply processing can be minimized. A final issue is circuit complexity and cost. Ideally, a simple, inexpensive power converter would enable rapid and precise changes in power supply. In practice, this ideal has proved unattainable. Further improvement is needed in order to achieve efficient, low-cost power amplifiers.